When a multilayer ceramic capacitor is used for decoupling around a CPU, an excessively low equivalent series resistance (ESR) of the multilayer ceramic capacitor causes the problem that oscillation due to parallel resonance occurs on a circuit, resulting in an increase in impedance. In order to avoid this problem, in the multilayer ceramic capacitor for use in the application, there has been a request to control the ESR to several 10 to several 1000 mΩ. As a multilayer ceramic capacitor satisfying the request, a multilayer ceramic capacitor having a resistive element in external electrodes has been proposed.
For example, Japanese Unexamined Patent Application Publication No. 11-54368 (Patent Document 1) discloses, as a CR composite electronic component, a multilayer ceramic capacitor having a specific resistance of external electrodes of 6.9×10−6 Ωcm or more, while causing a main composition of a conductive material in the external electrodes to contain at least one of Cu and Ni.
Japanese Unexamined Patent Application Publication No. 2001-223132 (Patent Document 2) discloses external electrodes including a three layer structure with a first conductive layer having oxidation-resistant metal, a second conductive layer formed thereon and including a mixture of a conductive oxide and an insulating oxide, and a third conductive layer formed thereon and including oxidation-resistant metal, to thereby increase ESR.
International Publication No. 2006/022258 document (Patent Document 3) discloses external electrodes including a conductive layer containing a complex oxide which reacts with Ni or a Ni alloy and a glass component in a multilayer ceramic capacitor including an internal electrode containing Ni or a Ni alloy. It also disclosed that use of an In—Sn complex oxide as the complex oxide is preferable.
However, the technique disclosed in each of Patent Documents 1 to 3 has following problems to be solved.
Since the external electrodes contain conductive metal, such as at least one of Cu and Ni, as a main component according to the technique disclosed in Patent Document 1, at least one of Cu and Ni sinter, causing metallic conduction to be dominant, and thereby obtainment of sufficient resistance (ESR) is difficult. Although Patent Document 1 also discloses increasing the resistance by adding a dissimilar metal to be alloyed, the increase in the resistance by such alloying is as small as about 10−6 Ω·cm to 10−4 or 10−5 Ω·cm. This indicates that, even when the external electrodes of a film thickness of 100 μm are formed on an end surface of a multilayer ceramic capacitor having a planar size of 20 mm×1.2 mm, for example, a resistive component of the external electrodes is about from 10−6 Ω·cm to 10−7 Ω·cm, and causes the development of sufficient resistance to be difficult.
In contrast, since the second conductive layer in the external electrodes contains, for example, a ruthenium oxide, a ruthenium oxide compound, or graphite as a main component, sufficient resistance can be obtained according to the technique disclosed in Patent Document 2. However, the technique disclosed in Patent Document 2 has a problem that since expensive metal, such as at least one selected from a group of Pd, Ag, Pt, Au, Rh, Ir, and Ru, for example is used as oxidation-resistant metal forming the first and third conductive layers of the external electrodes, the material cost of the first and third conductive layers increases. The technique disclosed in Patent Document 2 also has a problem that the external electrodes have a three layer structure and each of the first to third conductive layers is formed by being printed and has thick film thickness, so that the thickness of the whole external electrode increases to inhibit reduction in size of component.
The above-described problems encountered in the technique of each of Patent Documents 1 and 2 can be solved by the technique disclosed in Patent Document 3. Briefly, according to the technique of Patent Document 3, sufficient resistance can be obtained without requiring a three layer structure or expensive metal to be used.
However, weather resistance and bonding strength with an internal electrode of the conductive layer which is included in the external electrodes and contains a complex oxide reacting with Ni or a Ni alloy, such as an In—Sn complex oxide, and a glass component according to the technique disclosed in Patent Document 3, are not sufficient. Thus, a favorable bonding state is difficult to maintain against a thermal shock, bending, etc. Patent Document 3 also discloses addition of Ag to control resistance applied by the external electrodes. However, since Ag hardly has a solid solution region with the Ni contained in the internal electrode, the problem that bonding properties with the internal electrode decrease according to an increase of Ag arises. The problem of the favorable bonding with the internal electrode being impeded causes reduction of electrostatic capacitance applied by a multilayer ceramic capacitor.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-54368
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2001-223132
Patent Document 3: International Publication No. 2006/022258 document